1. Field of the Invention
The present invention relates to a process for producing a latex of a chloroprene polymer without using a conventional emulsifier. More particularly, the present invention concerns a process for polymerizing chloroprene by free radical polymerization in an aqueous medium in the presence of styrene sulfonic acid or a derivative thereof in the absence of an organic emulsifier.
2. Description of the Prior Art
The term "latex of a chloroprene polymer" as used herein refers to a latex of a homopolymer of chloroprene or a copolymer of chloroprene and a comonomer having an ethylenically unsaturated double bond, which is dispersed in water.
Latexes of chloroprene polymers have been produced in the past by polymerizing chloroprene in an aqueous medium in the presence of a conventional organic emulsifier, such as a metal salt of a rosin acid, sodium alkylsulfate, and the like. However, various disadvantages are encountered when conventional organic emulsifiers are used. For example, the polychloroprene latex has tendency to foam; and the physical properties and processability of chloroprene polymer prepared from the latex are often not satisfactory. In particular, it is known that the use of conventional organic emulsifiers are disadvantageous if the chloroprene polymer is to be used in a bonding composition. Further, the emulsifier solution is a potential pollution source and must be treated prior to discharge.
The conventional organic emulsifier is a low molecular weight compound which is only physical absorbed on latex particles. In order to overcome these disadvantages, it is necessary to prepare a latex which does not contain an emulsifier. Stabilized latexes of resinous polymers of styrene or methyl methacrylate have been prepared by using a polymerization initiator which contains a persulfate or a sulfonic acid group. Also stabilized latexes of styrene-butadiene polymers have been prepared by copolymerization with an unsaturated acid to introduce a carboxyl group. However, there is no known method for producing a stabilized polychloroprene latex which does not contain an emulsifier.
Accordingly, there exists a need for a process which can prepare stabilized chloroprene polymer latexes without the use of an emulsifier.
It was expected that the various disadvantages caused by a conventional organic emulsifiers could be alleviated by using a latex containing no emulsifier, however, it was totally unexpected that a stabilized latex would be prepared.